The present invention relates to phased array antennae, and more particularly, this invention relates to series fed phased array antennae.
Low cost phased array antennae are required on naval ships, land based radar stations and similar areas. Some traditional phased array antennae use periodic or spiral lattices and transmit/receive modules that are prohibitive in cost. When an antenna is designed for use with short wavelengths in advanced radar designs, a low side lobe architecture is required.
One type of phased array antenna architecture uses a Dual Application Program (DUAP) array structure based on a typical dual beam and corporate radio frequency and digital feed network. It typically includes a multilayer circuit board having various layers for different circuit components, including low noise amplifiers, phase shifters and other assorted feed lines, signal traces and component devices. For multiple beam and multiple polarization arrays, however, this type of antenna structure requires a complicated printed wiring board having multiple interconnects. For example, some printed wiring boards include over two thousand (2,000) vias in an 18-inch square printed circuit card, 64 elements, and two antenna beams. Not only is the layout of this array difficult to achieve, it can surpass some existing radio frequency layout tool capacities. This type of antenna architecture also requires a complicated feed network and multilayer circuit board with complicated circuit components that should not cross-over, thus, increasing design and construction difficulty.
Many phased array antennae use corporate feed networks with complicated interconnect systems because a corporate fed antenna allows a wide bandwidth. Also, in a planar array having a corporate feed network, the periodic spacing and phase settings between the antenna elements require only a simple sine calculation. The corporate feed network can typically provide an advantageous impedance match. Unfortunately, a corporate feed network is usually complicated and is often designed into an antenna structure from habit and not from advantage.
A linear, series fed array, however, will not have the complicated design drawbacks associated with a corporate feed network. Some linear, series fed arrays have been built as early as the 1940""s. For example, the United States Navy built a phased array series of fed WG slot arrays used to scan the beam. These type of linear, series fed arrays, however, were limited in their use because of frequency scan effects and the grating lobes.
In view of the foregoing background, it is therefore an object of the present invention to provide a series fed array antenna that overcomes the drawbacks associated with prior art linear series fed array antennae.
It is also an object of the present invention to provide a series fed antenna array that breaks up frequency scan effects and grating lobes.
It is yet another object of the present invention to provide a low cost antenna array that simplifies layout and eliminates crossover drawbacks associated complicated corporate feed networks.
These and other objects, features and advantages in accordance with the present invention are provided by a phased array antenna that includes a circuit board and a balanced, series fed antenna array formed from a plurality of antenna elements positioned in at least two spiral antenna arms on the circuit board. At least one signal feed point is positioned at a center portion of the spiral antenna arms for series feeding the antenna array, such that the antenna aids in breaking up frequency scan and grating lobes. In one aspect of the present invention, electronic circuitry can be supported by the circuit board and operatively connected to the antenna elements for amplifying, phase shifting and beam forming any transmitted or received signals.
In another aspect of the present invention, the antenna array is formed as two balanced series fed antenna arrays, each formed as spiral antenna arms and having dual feed points. The circuit board could be formed as a multilayer circuit board having a microstrip layer operative with the antenna elements for series driving the antenna array. The number of antenna elements within each spiral antenna arm are substantially the same and can be formed as either surface mounted antenna elements or printed antenna elements.
In yet another aspect of the present invention, the plurality of antenna elements are arranged on the circuit board in four spiral antenna arms as balanced, series fed antenna arrays having signal feed points at a center portion of the spiral arm. The antenna elements can be formed as respective 0, 90, 180 and 270 degree spiral arms for phased operation.
In yet another aspect of the present invention, the phased array antenna can comprise a balanced, series fed antenna array formed from a plurality of antenna elements positioned in at least two spiral antenna arms on the circuit board and having at least one signal feed point at a center portion of the spiral antenna arms for series feeding the antenna array. The spiral arms can be formed from a waveguide having slots defining the antenna elements. If a waveguide is not used, then the antenna elements can be positioned on a planar circuit board as described before.